Method for adapting the characteristic of an injection valve

ABSTRACT

The invention relates to a method for adapting an injection valve characteristic curve of a controlled fuel injection valve for an internal combustion engine, said curve reflecting the reference injection behaviour, to alterations in the actual injection behaviour caused by ageing. According to said method: during an operating mode of the internal combustion engine, which does not require an injection of fuel, the injection valve is intermittently controlled in accordance with a control period, said mode alternating with a period of no fuel injection, i.e. at least one working cycle with injection-valve control follows or precedes a working cycle without injection-valve control; at least one respective RPM value of the internal combustion engine is detected for the controlled working cycle and for at least one of the working cycles without control; a differential between the detected values is calculated and said differential is used to correct the characteristic curve.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method for adapting an injectionvalve characteristic, said characteristic representing a referenceinjection behavior, of a triggered fuel injection valve of an internalcombustion engine to aging-related changes or manufacturing-relatedvariations of an actual injection behavior.

For the purpose of fuel allocation, injection valves in internalcombustion engines are controlled in such a way that an optimal fuelquantity enters the combustion chambers at any operating point. Forexample, in the case of diesel internal combustion engines which areoperated with direct fuel injection, fuel that is under high pressure isinjected into the combustion chambers from a fuel accumulator. Themetering of the fuel quantity which is introduced into the combustionchamber is done by triggering the injection valves in a suitable manner,said injection valves also being referred to as injectors. The meteringis usually time-controlled in this case, i.e. the injection valve isopened for a precisely specified time and then closed again. A controldevice of the internal combustion engine predetermines an openinginstant and an opening duration of the injection valve. A control signalis applied to e.g. an electrically activated injection valve in thiscase, wherein said signal predetermines a trigger duration.

The control device can effect an assignment between the trigger durationand the metered fuel mass; an injection valve characteristic is storedfor this purpose in the control device, and establishes a relationshipbetween the injected fuel quantity and the trigger duration of theinjection valve, wherein other conditions such as fuel pressure or fueltemperature are also taken into consideration.

The injection valve characteristic assumes a standard injection valvewhich corresponds to certain specifications. However, since theinjection behavior of each individual injection valve always variesslightly in principle, certain differences arise with regard to thedelivered fuel volume from injection valve to injection valve in thecase of fixed trigger durations. This results in irregular running ofthe internal combustion engine and, above all, in poor exhaust values.In order to ensure that strict exhaust standards can nonetheless be met,the permitted tolerances for the injection valves must be kept as low aspossible, this being very expensive.

Even then, however, aging-related wear effects of the injection valvecan cause variations to occur between the actual injection behavior andthe reference injection behavior as specified in the injection valvecharacteristic. In order to compensate for such variations, it would beconceivable in principle to modify the stored injection valvecharacteristic during the service life of the internal combustion enginein a controlled manner towards a reference injection behavior for anaged reference injection valve. However, such a simply controlled andtherefore very unspecific modification could not take into considerationthe individual characteristics of an injection valve. Furthermore,significant problems arise if an injection valve is replaced during theservice life of an internal combustion engine.

Alternatively, it would be conceivable to provide an additional knocksensor, by means of which the combustion noise of the internalcombustion engine is monitored. It would then be possible to determinethe trigger time which is required for implementing a combustion noise.However, it is still only possible to determine a minimal trigger timeat which the injection valve starts to deliver a fuel mass in a stablemanner. Moreover, this method is relatively imprecise. It is also veryexpensive because an additional sensor including a corresponding signalcapture circuit must be provided.

SUMMARY OF THE INVENTION

The invention therefore addresses the problem of specifying a method foradapting an injection valve characteristic, said characteristicrepresenting a reference injection behavior, of a triggered fuelinjection valve of an internal combustion engine to aging-relatedchanges of an actual injection behavior, which method allows anindividual adaptation to be performed for each injection valve.

In accordance with the invention, this problem is solved by a method foradapting an injection valve characteristic, said characteristicrepresenting a reference injection behavior, of a triggered fuelinjection valve of an internal combustion engine to aging-relatedchanges of an actual injection behavior, wherein during an operatingstate of the internal combustion engine, which operating state does notrequire a fuel injection, the injection valve is triggeredintermittently in accordance with a trigger duration, while otherwise nofuel injection occurs, such that at least one work cycle with triggeringfollows or precedes at least one work cycle without triggering of theinjection valve, a rotational-speed value or a value of arotational-speed-dependent variable of the internal combustion engine isdetected in each case for the work cycle with triggering and for atleast one of the work cycles without triggering and a difference betweenthe detected values is established and a correction of the injectioncharacteristic is effected thereupon.

In accordance with the invention, therefore, the injection valve isintermittently triggered in accordance with a trigger duration during anoperating state of the internal combustion engine, which operating statedid not actually require a fuel injection. Therefore a work cycle withtriggering of the injection valve alternates with a work cycle in whichthe injection valve is not triggered, i.e. the internal combustionengine runs entirely without fuel injection. This results in a switchingon and switching off of the injection valve whose injection behaviormust be adapted. As a result of the comparison of the rotational-speedvalue or rotational-speed-dependent value, which comparison is thenperformed in accordance with the invention, a correction of theinjection characteristic is effected. The rotational-speed informationwhich is analyzed in this regard, being either the rotational speeditself or a rotational-speed-dependent variable, changes if an injectionoccurs which generates an angular momentum. The change is dependent onthe injected fuel mass in this case, and therefore it is possible tocorrect not only the implementation of an injection above a certainminimal trigger duration but also the complete injection characteristic,i.e. the dependency of the fuel mass that is delivered by the injectionvalve on the trigger duration.

In order to adapt the complete injection characteristic of the injectionvalve to the actual injection behavior, it is obviously necessary toperform an injection over the widest possible range of trigger durationsand other injection parameters such as fuel pressures, for example. Itis therefore preferable to increase the trigger duration step-by-step,wherein the step size is dependent on the desired accuracy of thecorrection of the injection valve characteristic. Two steps, with whicha check is performed using a minimal and a maximal trigger duration, aresufficient in principle, for example.

The fuel mass which is delivered by the injection valve causes theinternal combustion engine to deliver an angular momentum. This angularmomentum is naturally shown in the rotational-speed information. Ratherthan analyzing the rotational-speed information directly, however, it isexpedient to first calculate an angular momentum value for an angularmomentum which was caused by the triggering of the injection valve withthe trigger duration. The calculation of this angular momentum value hasthe advantage that the value which is ultimately sought for the fuelmass can then be obtained by means of a simple conversion. Thecorresponding ratios for this are generally stored in the control deviceof the internal combustion engine, since modern control devices normallyperform a so-called angular momentum-based control in which a preferredangular momentum is determined and a fuel mass is derived therefrom.Therefore if a angular momentum value is specified, as in the preferredembodiment, the conversion which is used anyhow in the angularmomentum-based control simply has to be applied in the oppositedirection.

The specification of the angular momentum value can be done by means ofa suitable analysis of the rotational-speed gradient. If an internalcombustion engine runs under overrun cut-off, the rotational speed willgenerally decrease. It is evident that a rotational-speed gradient forwork cycles in which the injection valve, whose injection valvecharacteristic is to be adapted, is triggered is different to that forwork cycles in which there is no activation of the injection valvewhatsoever. Analysis of the rotational-speed gradient therefore allowsthe aforementioned angular momentum value to be generated easily.

In a preferred embodiment, the angular momentum value is thereforecalculated in accordance with the following formula:D=(π/F1).M.(dN+−dN−)+dJ,where F1 is a factor that is dependent on a number of cylinders, D isthe angular momentum value, M is the moment of inertia of the internalcombustion engine, dN+ is a rotational-speed gradient of the work cyclewith triggering of the injection valve, dN− is a rotational-speedgradient of one of the work cycles without triggering of the injectionvalve, and dJ is a factor for a braking moment which is caused byinternal friction of the internal combustion engine and can be dependenton the rotational speed.

The difference between the rotational-speed gradient of the work cyclewith triggering of the injection valve and of one of the work cycleswithout triggering of the injection valve is therefore a suitablevariable for the calculation of the angular momentum in a preferredembodiment. The equation can be applied to internal combustion engineswith any number of cylinders. Depending on the number of cylinders, adifferent prefactor F occurs. In the case of four cylinders, F1=30.

The moment of inertia M of the internal combustion engine is influencedby the centrifugal mass of pistons, crankshaft, camshaft and possiblecentrifugal masses, and represents a variable which is fixed andunchanging for an internal combustion engine.

The braking moment of the internal combustion engine is caused byinternal friction and is generally also a largely constant variablewhich can be determined easily on a testing stand in the same way as themoment of inertia. In order to make the effect of the rotational-speedgradient as great as possible, it is advantageous to minimize thebraking moment. To this end, for example, a drive train which is drivenby the internal combustion engine can be disconnected for the purpose ofthe method for adapting the injection valve characteristic, e.g. byactivating a corresponding clutch.

Furthermore, in order to improve the signal/noise ratio, the claimedmethod, i.e. the intermittent triggering of the injection valve and thetriggering of the rotational-speed information, can be executed severaltimes with an unchanged trigger duration.

In the case of multi-cylinder internal combustion engines, a segmentwheel which has a divisional structure and is driven by the internalcombustion engine is usually sampled and the rotational-speedinformation is captured in the form of segment times for which thepassage of a specific segment of the segment wheel lasts. In this case,a segment is normally allocated to the working stroke of a cylinder ofthe multi-cylinder internal combustion engine. Given a rotational-speedcapture of this type, it is particularly easy to determine thedifference between the segment times for a cylinder without and withtriggering of the injection valve and to use said difference foradapting the injection valve characteristic.

In this regard, a method is therefore preferred in which a segment wheelthat is driven by the internal combustion engine is sampled and a firstwork cycle without triggering of the injection valve of a specificcylinder then a second work cycle with triggering of the injection valveof the specific cylinder and then a third work cycle without triggeringof the injection valve of a specific cylinder are executed, wherein asegment time is determined in at least the first, second and third workcycle for the specific cylinder, said segment time being the duration ofthe passage of a segment of the segment wheel during the working strokeof the cylinder, and wherein the angular momentum is calculated inaccordance with the following equation:D=F2.π.M((Tx3−Tx2)/(ST−)³)−(Tx2−Tx1)/(ST+)³)+dJ,where F2 is a factor that is dependent on the number of cylinders, D isthe angular momentum value, M is the moment of inertia of the internalcombustion engine, dJ is a factor for a braking moment which is causedby internal friction of the internal combustion engine, Tx1 is thesegment time for the specific cylinder in the first work cycle, Tx2 isthe segment time for the specific cylinder in the second work cycle, Tx3is the segment time for the cylinder in the third work cycle, ST− is theaverage total duration of the passage of all segments during a workcycle without triggering of the injection valve, and ST+ is the averagetotal duration of the passage of all segments during one of the workcycles with triggering of the injection valve.

In this embodiment, it is usual to make use of the average totalduration of the passage of all segments for the working cycle in whichthe segment times specified in the denominator of the equation were alsoobtained. This is not essential, however, and other total durations,e.g. from previous work cycles, can also be used depending onrotational-speed capture.

Going beyond the above equation, it is also possible to calculate andanalyze higher divisional orders of the segment times in the form ofdifference quotients, in order to increase the accuracy of the angularmomentum or injection-volume specification. Using signal-analysismethods, it is also possible to analyze the overall profile of therotational-speed decrease over a larger number of work cycles with andwithout injection, in order thus to identify and eliminate interferenceeffects such as torsional vibrations of the drive train and thereforeagain to increase the accuracy of the calculation of the angularmomentum or injection volume.

In the aforementioned developments for calculating the angular momentumvalue D, a factor is used for a braking moment which is caused byinternal friction of the internal combustion engine. A particularlyaccurate assessment of this factor, which is additionally included inthe equations, is obtained by using the braking moment for the relevantwork cycle in which the injection valve was triggered or not triggered.In this regard, a preferred method for determining the factor for thebraking moment which is caused by the internal friction of the internalcombustion engine therefore provides for establishing a differencebetween two values, wherein one value is assigned to one of the workcycles of the internal combustion engine without triggering of theinjection valve and the other is assigned to the work cycle of theinternal combustion engine with triggering of the work cycle.

In most cases, the injection valve characteristic which must be adaptedto the actual injection behavior of an injection valve is present in theform of a link between fuel mass and trigger duration. For the purposesof the adaptation in such cases, it is preferable for a fuel-mass valuerelating to a fuel mass which is delivered by the injection valve to bederived from the rotational-speed value or the angular momentum value,and for said fuel-mass value to be assigned to the value for the triggerduration for which the fuel-mass value was obtained. By means of thisassignment, it is then possible easily to correct an injection valvecharacteristic, said correction containing the aforementioned mappingbetween trigger duration and fuel-mass value.

BRIEF DESCRIPTION OF THE DRAWING

The invention is described in greater detail below for exemplarypurposes with reference to the drawing, in which:

FIG. 1 shows a diagram in which a fuel mass which is delivered by aninjection valve is plotted over the trigger duration of the injectionvalve,

FIG. 2 shows two diagrams in which the rotational speed of the internalcombustion engine or the revolution duration of a segment wheel which isconnected to the crankshaft of an internal combustion engine are plottedas a time series which is produced when the claimed method is executed,

FIG. 3 shows a detailed section of the illustration from FIG. 2, and

FIG. 4 shows the fuel mass which is delivered by an injection valve as afunction of the trigger duration of the injection valve, together withmeasuring points which are used for the correction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the injection valve characteristic of an electricallytriggered injection valve of an internal combustion engine (not shown).In this case, a fuel mass K is plotted over a trigger duration TI. Theinjection valve is triggered to deliver a fuel mass by means of acorresponding electrical trigger signal, i.e. the control deviceinstructs the injection valve which is supplied by a fuel accumulator toopen for the trigger duration TI. Due to mechanical and electricalfactors, however, the injection valve will only then follow above acertain minimal trigger duration which is illustrated in FIG. 1 as startvalue TI_(—)0. Shorter trigger durations cannot be achieved. If thestart value TI_(—)0 is exceeded, the injection valve delivers a fuelmass which depends on the trigger duration in accordance with thecharacteristic as shown in FIG. 1. The characteristic 1 which is shownas a broken line in FIG. 1 is stored in the control device in the caseof a newly supplied internal combustion engine and assumes a referenceinjection behavior of a new value injection valve which satisfiesspecific specifications.

Also illustrated in FIG. 1 as a continuous line is an exemplarycharacteristic 2 of an aged injection valve. It can be seen that thestart value TI_(—)0, which a trigger duration TI must exceed in order tocause a fuel mass to be delivered by the injection valve, is greaterthan the start value for the reference injection behavior as percharacteristic 1. Due to manufacturing tolerances and/or changes whichoccur during the service life of the injection valve as a result of weareffects or similar, a shift dTI appears between the start points. As aresult of this shift, a different trigger duration TI is required in thecase of an injection valve having the characteristic 2 to that which isrequired in the case of a reference injection valve having thecharacteristic 1, in order to deliver the same fuel mass. The shift canextend over longer or shorter trigger durations depending onaging/manufacturing nonconformity.

The deviation from the characteristic 1 which is provided as a basis bythe control device during the control results in a degraded performanceand exhaust behavior of the internal combustion engine. In theadaptation which is outlined below, this deviation is rectified bycorrecting the reference characteristic 1 in such a way that it isidentical to the actual characteristic 2.

The illustration in FIG. 1 suggests that, in order to adapt the actualinjection behavior as per characteristic 2 to the reference injectionbehavior as per characteristic 1, it could suffice to determine theshift dTI. This might indeed suffice in most cases, but aging effectswhich are caused by wear at the injection valve can also prevent thecharacteristic 2, which represents the injection behavior, from beingobtained from the characteristic 1 of the reference injection behaviorby means of a simple parallel shift along the x axis. Further variationsbetween the characteristics 1 and 2 can also arise due to aging. This isclear e.g. from the profile of the characteristic 1 in the area ofhigher trigger durations TI; in this section the shift between thecharacteristic 1 and the characteristic 2 is smaller than in the area oflower fuel masses K or in the area of the start value TI_(—)0.

In order now to adapt the characteristic 1 which is used in the controldevice of the internal combustion engine to the actual injectionbehavior as per characteristic 2, the fuel mass K which is delivered bythe relevant injection valve is determined as a function of the triggerduration TI in an adaptation method.

An overrun cut-off phase of the internal combustion engine is used forthis purpose, in which phase the internal combustion engine is alsoseparated from an external drive train of the vehicle which is driven bythe internal combustion engine by means of releasing a clutch in orderto eliminate external braking moments. The internal combustion engine isessentially operated without fuel in the overrun cut-off phase, wherebythe rotational speed decreases sharply until an idle controllerintervenes in order to stabilize the operation of the internalcombustion engine at idle speed.

In this case, “essentially” operated without fuel supply is understoodto mean that a fuel supply only occurs for the purpose of the adaptationmethod, but is not actually desired or required in this operating state.

In order to adapt the characteristic of the injection valve, theinjection valve is intermittently triggered in accordance with a triggerduration in the overrun cut-off phase, i.e. work cycles of the internalcombustion engine, in which work cycles the injection valve is triggeredto open for a specific trigger duration, alternate with work cycles inwhich the injection valve is not activated.

By means of a time series in each case, FIG. 2 shows the profile of therotational speed N of the internal combustion engine and of a revolutionduration U of a segment wheel which is driven by the internal combustionengine and is non-rotatably connected to the crankshaft of the internalcombustion engine. The rotational-speed profile is illustrated with atrigger signal 4 in the left-hand time series of FIG. 2. Therotational-speed profile 3 represents the time-related development ofthe rotational speed of the internal combustion engine. The triggersignal 4 is the signal by means of which an injection valve is triggeredduring the overrun cut-off of the internal combustion engine. Thetrigger signal 4 is composed of trigger pulses 5 and intermediate pauses6. During the time duration of a trigger pulse 5, the injection valve istriggered in accordance with a trigger duration. If this is greater thanthe start value TI_(—)0 the injection valve opens and a cylinder of theinternal combustion engine, which cylinder is supplied by the injectionvalve, executes a working stroke because fuel is allocated. Workingstrokes of the cylinder which are in the pauses 6 take place without theinjection valve being triggered to open. These are therefore workingstrokes in which the corresponding cylinder is disconnected.

The trigger signal 4 therefore represents a binary signal whichindicates whether the injection valve whose characteristic must beadapted is actually triggered. The width of the trigger pulse 5 in FIG.2 does not represent the trigger duration, but merely indicates whetherthe injection valve is triggered in a work cycle.

Since the internal combustion engine is in an overrun cut-off phase, therotational speed N decreases. However, this decrease takes place withvarying gradients, since an injection valve is intermittently triggeredby the trigger pulses 5.

The rotational-speed profile 3 exhibits a lesser slope in work cyclesfor which a trigger pulse 5 is drawn, i.e. in which the injection valveopens, than when the trigger signal indicates a pause 6, i.e. theinjection valve remains closed. The sections with a lesser slope aremarked with a “+” and given the reference sign 7. The sections with agreater gradient, i.e. with a faster decreasing rotational-speed profileare marked with a “−” and have the reference sign 8.

In addition to the trigger signal 4, the right-hand illustration in FIG.2 shows a passage-duration profile which represents the time-relateddevelopment of the revolution duration U of the segment wheel. Therevolution duration U is inversely proportional to the rotational speedN. In the sections 7 of the passage duration profile 9, the revolutionduration increases less than in the sections 8, this being againconditional upon the triggering of the injection valve which indicates atrigger pulse 5 during the sections 7 and a pause 6 in the sections 8.

The lesser slope of the rotational-speed profile 3 in the phases 7 inwhich the injection valve is triggered with a trigger duration accordingto the trigger pulse 5 stems from the fact that due to the fuelinjection the corresponding cylinder of the internal combustion enginedelivers an angular momentum. This angular momentum contribution dependson the trigger duration with which the injection valve is triggered inthe trigger pulses and is determined as per the following equation in afirst embodiment:D=(π/F).M.(dN+−dN−)+dJ,where F is a factor that is dependent on a number of cylinders, D is theangular momentum value, M is a moment of inertia of the internalcombustion engine, dN+ is a rotational-speed gradient of the work cyclewith triggering of the injection valve, dN− is a rotational-speedgradient of one of the work cycles without triggering of the injectionvalve, and dJ is a factor for a braking moment which is caused byinternal friction of the internal combustion engine. The factor F hasthe value 30 for a four-cylinder internal combustion engine. Therotational-speed gradient dN+ is given by the slope of therotational-speed profile 3 in the section 7 and the rotational-speedgradient dN− by the slope of the sections 8 of the rotational-speedprofile 3.

The factor dJ takes into consideration a braking moment which is causedby internal friction of the internal combustion engine. When the drivetrain is disconnected, this braking moment depends solely on theconstruction or operating parameters of the internal combustion engineitself and can be taken from a characteristic map, for example. Thebraking moment is particularly dependent on the rotational speed, andtherefore in an alternative embodiment two values are determined and thedifference is established for the braking moment at the averagerotational speed in the section 7 and section 8, said sections beingused for the calculation of the angular momentum as per the aboveequation, wherein when establishing the difference the braking moment atthe instant when dN− was determined is subtracted from the brakingmoment at the instant when dN+ was determined in order to specify thefactor dJ.

The angular momentum value D as calculated using the above equationrepresents the angular momentum which was generated by the triggering ofthe injection valve with the trigger duration that was used for theadaptation. This angular momentum can be converted into the desired fuelmass K in a manner which is known to a person skilled in the art, e.g.by means of a characteristic map.

The described adaptation is now repeated for various trigger durationsin order to obtain a set of value pairs which consist in each case of anangular momentum value and a trigger duration or a fuel-mass value and atrigger duration. FIG. 4 shows the outline of the value pairs which areobtained for an exemplary injection valve. The fuel mass K (in mg) isplotted over the trigger duration TI (in ms). A fuel mass of 1 mg isdelivered in the case of a trigger duration of slightly more than 0.16ms.

Each measuring point corresponds to one execution of the method foradaptation given a specific trigger duration, wherein the angularmomentum calculated as described above was also converted by means of aknown connection into a fuel mass that was delivered by the injectionvalve in the method for adaptation. It can be seen that the injectionvalve only starts to deliver a fuel mass above a certain triggerduration. The lower limit corresponds to the start value TI_(—)0 inFIG. 1. The illustration in FIG. 4 also shows that the resolution forthe adaptation is in the range of 0.1 to 0.2 mg.

The curve 14 which is illustrated in FIG. 4 can therefore be used as acharacteristic 1 which is assigned to the corresponding injection valvein the operation of the internal combustion engine, or for correctingthe characteristic 1 in accordance with the curve 14. In this regard,FIG. 4 shows a small section of the characteristic 2 from the FIG. 1around the start value TI_(—)0.

FIG. 3 illustrates a second embodiment of the method with which anadaptation of the injection valve characteristic can be achieved. Inthis case, FIG. 3 shows a section of the passage duration profile 9 ofthe right-hand illustration from FIG. 2. Consecutive sections 7 and 8are illustrated in a section of the passage duration profile 9 in FIG.3, wherein each section corresponds to a work cycle. A segment signal 10is also shown and represents the segment durations for which the passageof a segment of the segment wheel lasts, wherein each segment isassigned to exactly one cylinder of a four-cylinder internal combustionengine. The corresponding work sequence of the cylinders is also plottedusing Roman numerals on the time axis which shows the time t. Theinternal combustion engine which is considered in the example thereforehas the work cycle sequence IV, I, II and III. This is the sequence inwhich the cylinders of the four-cylinder internal combustion engineexecute their working strokes within a work cycle.

The characteristic of the cylinder I is adapted in the followingadaptation method.

In three consecutive work cycles 11 to 13, the injection valve of thecylinder I is first triggered in accordance with a trigger duration in afirst work cycle 11. In the subsequent second work cycle 12, there is notriggering of the injection valve of the cylinder I, i.e. the triggersignal 4 specifies a pause 6. In the subsequent third work cycle 13, thetrigger signal 4 specifies a trigger pulse 5 again, i.e. the injectionvalve of the cylinder I is again triggered in accordance with a triggerduration, this being the same trigger duration as in the work cycle 11.The sections 7, 8 and again 7 of the passage duration profile 9 areproduced by the sequence from the first work cycle 11 to the third workcycle 13.

The associated segment time T is plotted for each work cycle of thecylinders I, II and III in FIG. 3, wherein a suffix of two Arabicnumerals is also added, of which the first numeral represents thecylinder number and the second numeral represents the work cycle (1:first work cycle, 2: second work cycle, 3: third work cycle).

FIG. 3 shows clearly that as a result of the triggering of the injectionvalve of the first cylinder in the first work cycle and the third workcycle, T11 and T13 are much shorter than the segment time T12 in thesecond work cycle in which the injection valve of the cylinder I is nottriggered. The shorter segment times T11 and T13 are therefore producedbecause the cylinder I delivers a angular momentum in the first workcycle 11 and in the third work cycle 13. This in turn is due to theinjection valve introducing a fuel mass into the combustion chamber ofthe cylinder I as a result of the triggering with a trigger duration.

The angular momentum which is produced by this injection is nowcalculated according to the following equation:D=F2.π.M((Tx3−Tx2)/(ST−)³)−(Tx2−Tx1)/(ST+)³)+dJ,where F2 is a factor that is dependent on the number of cylinders (16 inthe case of a four-cylinder internal combustion engine), D is theangular momentum value, M is the moment of inertia of the internalcombustion engine, dJ is a factor for a braking moment which is causedby internal friction of the internal combustion engine, Tx1 is thesegment time for the specific cylinder in the first work cycle, Tx2 isthe segment time for the specific cylinder in the second work cycle, Tx3is the segment time for the cylinder in the third work cycle, ST− is theaverage total duration of the passage of all segments during a workcycle without triggering of the injection valve and ST+ is the averagetotal duration of the passage of all segments during one of the workcycles with triggering of the injection valve.

The above statements in relation to the first embodiment apply to themoment of inertia of the internal combustion engine and to the factordJ. In this case, the difference for calculating the factor dJ can bedetermined using the equationdJ=J(120/ST−)−J(120/ST+),for example, wherein a segment wheel having 120 part segments or teethis assumed and J designates the rotational-speed-dependent brakingmoment of the internal combustion engine. This value is stored forexecuting the adaptation in the control device of the internalcombustion engine and is obtained from a testing stand measurement, forexample.

As in the aforementioned first exemplary embodiment, the value pair isformed from the angular momentum value and the associated triggerduration. The value pairs for different trigger durations then allow acorrection of the reference injection valve characteristic, if necessaryafter converting the angular momentum values into values for fuelmasses.

1. A method for adapting an injection valve characteristic, theinjection valve characteristic representing a reference injectionbehavior, of a triggered fuel injection valve of an internal combustionengine to aging-related changes or manufacturing-related variations ofan actual injection behavior, which comprises the steps of: a) during anoperating state of the internal combustion engine, the operating statenot requiring a fuel injection, triggering an injection valveintermittently in accordance with a trigger duration, while otherwise nofuel injection occurs, such that at least one work cycle with triggeringfollows or precedes at least one work cycle without triggering of theinjection valve; b) detecting a rotational-speed value or a value of arotational-speed-dependent variable of the internal combustion engine ineach case for the work cycle with triggering and for at least one of thework cycles without triggering; and c) establishing a difference betweendetected values and a correction of the injection valve characteristicbeing effected thereupon.
 2. The method according to claim 1, whichfurther comprises calculating derivatives of a first and/or higher orderfrom the differences between the detected values.
 3. The methodaccording to claim 2, which further comprises: calculating thedifferences on a basis of measured segment times; calculating differencequotients from the differences; and deriving the derivatives of thefirst and higher order therefrom.
 4. The method according to claim 1,which further comprises: analyzing an overall profile of therotational-speed value or of the rotational-speed-dependent variableusing signal-analysis methods over a plurality of the work cycles withand without triggering; and identifying and eliminating interferenceeffects.
 5. The method according to claim 1, which further comprisesincreasing the trigger duration step-by-step.
 6. The method according toclaim 1, which further comprises during the establishing of thedifference step, calculating an angular momentum value for an angularmomentum which was produced by triggering of the injection valve withthe trigger duration.
 7. The method according to claim 6, which furthercomprises calculating the angular momentum value in accordance with thefollowing formula:D=(_(π) /F1)*M*(dN+−dN−)+dJ, where F1 is a factor that is dependent on anumber of cylinders, D is the angular momentum value, M is a moment ofinertia of the internal combustion engine, dN+ is a rotational-speedgradient of the work cycle with triggering of the injection valve, dN−is a rotational-speed gradient of one of the work cycles withouttriggering of the injection valve, and dJ is a factor for a brakingmoment which is caused by internal friction of the internal combustionengine.
 8. The method according to claim 7, which further comprisesestablishing a difference between two values for determining a factorfor the braking moment which is caused by the internal friction of theinternal combustion engine, wherein one value is assigned to one of thework cycles of the internal combustion engine without triggering of theinjection valve and the other is assigned to the work cycle of theinternal combustion engine with triggering of the work cycle.
 9. Themethod according to claim 6, which further comprises: using amulti-cylinder internal combustion engine as the internal combustionengine; sampling a segment wheel driven by the internal combustionengine; executing a first work cycle without triggering of the injectionvalve of a specific cylinder, then a second work cycle with triggeringof the injection valve of the specific cylinder, and then a third workcycle without triggering of the injection valve of the specificcylinder, wherein a segment time is specified in at least the first,second and third work cycle for the specific cylinder, the segment timelasting for a passage of a segment of the segment wheel during a workingstroke of the specific cylinder; and calculating the angular momentum inaccordance with the following equation:D=F2*_(π) *M((Tx3−Tx2)/(ST−)³)−(Tx2−Tx1)/(ST+)³)+dJ  where F2 is afactor that is dependent on a number of cylinders, D is the angularmomentum value, M is a moment of inertia of the internal combustionengine, dJ is a factor for a braking moment which is caused by internalfriction of the internal combustion engine, Tx1 is the segment time forthe specific cylinder in the first work cycle, Tx2 is the segment timefor the specific cylinder in the second work cycle, Tx3 is the segmenttime for the cylinder in the third work cycle, ST−is a average totalduration of a passage of all segments during a work cycle withouttriggering of the injection valve and ST+ is an average total durationof a passage of all segments during one of the work cycles withtriggering of the injection valve.
 10. The method according to claim 6,which further comprises: deriving a fuel-mass value for a fuel mass thatis delivered by the injection valve from the angular momentum value;assigning the fuel-mass value to the trigger duration and used forcorrecting the injection valve characteristic.
 11. The method accordingto claim 1, which further comprises executing the steps a) and b)several times with an unchanged trigger duration for providing noisesuppression.